Two Young Girls Posing With The Old Airplane

A propeller or airscrew comprises a set of small, wing-like aerofoils set around a central hub which spins on an axis aligned in the direction of travel. Spinning the propeller creates aerodynamic lift, or thrust, in a forward direction.
A tractor design mounts the propeller in front of the power source, while a pusher design mounts it behind. Although the pusher design allows cleaner airflow over the wing, tractor configuration is more common because it allows cleaner airflow to the propeller and provides a better weight distribution.
A contra-prop arrangement has a second propeller close behind the first one on the same axis, which rotates in the opposite direction.
A variation on the propeller is to use many broad blades to create a fan. Such fans are traditionally surrounded by a ring-shaped fairing or duct, as ducted fans.